This invention relates generally to paper making machines and, more particularly, to apparatus for facilitating the conveyance of a lead-in strip of a web.
When the operation of a paper machine is initiated, their, when the paper machine is first started or when the paper machine is restarted, such as after a web break, a relatively narrow lead-in strip is cut from the leading end of the web such, for example, as by directing a water spray against the web while it is positioned against a stone cylinder. The narrow lead-in strip, which may for example have a width of about 200 mm, is then manually guided into the web lead-in equipment, such guidance being facilitated by means of air jets. The web lead-in equipment of the drier part of the paper machine conventionally comprises a double rope mechanism arranged so that each drier section of the drier part is equipped with ropes which run over pulleys installed near the ends of the drying cylinders. Although the web lead-in strip is normally guided between two ropes, as many as three cooperating ropes or belts have been used in single-wire lead-in arrangements.
In the press part of the paper machine, the web lead-in strip is normally manually pulled to the side of the paper machine between the ropes without the assistance of air jets. This operation can be somewhat dangerous as it must of necessity be performed close to massive rotating machine components. The operation also requires considerable skill.
The difficulties in conveying and guiding the web lead-in strip described above have become more serious as the speeds of paper machines increase. The difficulties are most serious immediately after the press part, in the preliminary drier part, and in the gaps between the drier sections of the dryer part.
An arrangement for controlling the conveyance and guidance of a web lead-in strip at the drier part of a paper machine is disclosed in U.S. application Ser. No. 653,825 filed Sept. 24, 1984, now U.S. Pat. No. 4,543,160, assigned to the assignee of the instant application. In the arrangement disclosed in said Patent, the web lead-in strip is detached from a cylinder of the press part of the paper machine by means of air jets and is guided by means of additional air jets into contact with the drying wire of the dryer part. Subsequently, air jets are applied to the lead-in strips supported by the drying wire in order to separate the lead-in strip from the drying wire. Substantially immediately thereafter, transverse air jets are directed onto the lead-in strip whereby the lead-in strip is moved into position within the gap formed between the lead-in ropes whereupon the web is carried over the drying cylinders.
Concerning the state of the art relative to the present invention, reference is made to Finnish Pat. No. 57 990 and U.S. Pat. No. 3,355,349. A belt conveyor for a calender or a reel-up for conveying the lead-in strip, or a belt conveyor arranged before the calender are disclosed in these patents. Such known belt conveyor arrangements comprise two reversing rolls and a closed air-pervious belt loop having an upper run which is subjected to a vacuum created by a suction box positioned within the belt loop. The suction box creates a vacuum on the upper run of the belt which holds the lead-in strip in contact with the conveyor belt. A major drawback of these conventional arrangements is that it is difficult to seal the suction box to obtain a sufficient vacuum. Moreover, the suction box is a heavy component having a relatively complicated construction.
With further reference to the state of the art with respect to the present invention, reference is also made to Finnish Pat. No. 62 695 which corresponds to No. DOS-3218306 and U.S. Pat. No. 4,501,643, assigned to applicant's assignee. An arrangement is disclosed in this patent for a cutting and guiding device which comprises guide plates provided with air jet means for guiding and supporting a lead-in strip. A drawback of this known device is that relatively wet paper webs tend to stick to the air jet plates so that the web lead-in operation is not always successful.